perf(planner): load the PDF export and the transport modal on demand (#1821)

Two more things every trip paid for whether or not anyone used them.

downloadTripPDF hung statically off the days sidebar, so opening any trip
pulled in the whole PDF builder. Both call sites are already async and already
wrap the call in try/catch, so a failed chunk surfaces as the export error the
handler had anyway.

TransportModal was already rendered conditionally, which means lazy bites
immediately. It is worth more than its own 32 kB: it is the only path to
TransitSearchPanel, and that chunk carried tz-lookup — about 200 kB of packed
zone geometry.

  TripPlannerPage      339.78 -> 305.70 kB
  entry chunk          258.24 -> 218.70 kB
  TransitSearchPanel   198.67 ->  26.51 kB   (and now on demand)
  TripPDF              226.02 ->  27.78 kB   (and now on demand)
  eager path           unchanged at 1,483 kB

Worth stating plainly: tz-lookup itself did not go away. It sits in
PlaceFormModal.helpers now, and PlaceFormModal is still a static import of the
planner, so a trip still loads it. Prying that loose means touching
placeOpenState, whose consumers assume a synchronous lookup — a separate change
with its own care.

client/src/components/Planner/DayPlanSidebarToolbar.tsx

@@ -1,6 +1,5 @@
 import React, { useState, useRef } from 'react'
 import { ChevronsDownUp, ChevronsUpDown, FileDown, Undo2, ArrowUpDown, CalendarPlus, Route as RouteIcon } from 'lucide-react'
-import { downloadTripPDF } from '../PDF/TripPDF'
 import { DayReorderPopup } from './DayReorderPopup'
 import Tooltip from '../shared/Tooltip'
 import { useToast } from '../shared/Toast'
@@ -79,6 +78,11 @@ export function DayPlanSidebarToolbar({
                 notes.map(n => ({ ...n, day_id: Number(dayId) }))
               )
               try {
+                // Loaded on click: the PDF builder is ~226 kB and hangs off the
+                // days sidebar, so every trip used to pay for it whether or not
+                // anyone exported. A missing chunk lands in the catch below and
+                // shows the same error the export already had.
+                const { downloadTripPDF } = await import('../PDF/TripPDF')
                 await downloadTripPDF({ trip, days, places, assignments, categories, dayNotes: flatNotes, reservations, t, locale })
               } catch (e) {
                 console.error('PDF error:', e)